There have so far been well-known processes for forming a color proof from a plurality of black-and-white half dot images prepared by a color-separation and a half dot image conversion in a color plate-making.printing process. These processes include an over-lay process in which a color image is formed by making use of a photopolymer or a diazo compound, and a surprint process.
The over-lay process has the advantage that the operations are very simple and the production cost is low. The process can be utilized for proofing by superposing four color film sheets (in the primary colors of subtractive color mixture and black). However, this process has a disadvantage that a gloss is produced by superposing the film sheets and, therefore, the resulting texture becomes different from printed matter.
The surprint process is to superpose colored images on a support. This type of process include the well-known processes described in, for example, U.S. Pat. Nos. 3,582,327, 3,607,264 and 3,620,726, in which a colored image is obtained by utilizing the adhesiveness of photopolymeric materials and carrying out a toner development.
There are also the well-known processes as described in Japanese Patent Examined Publication No. 47-27441/1972 and Japanese Patent Publication Open to Public Inspection (hereinafter abbreviated to JP OPI Publication) No. 56-501217/1981, in which a color proof is prepared in the following manner. An image is formed by transferring it onto a support by making use of a light-sensitive colored sheet, by exposing it to light and then by developing it. After that, another colored sheet is laminated thereon and then the same procedures are repeated so as to prepare the color proof.
There is also a-well-known process as described in JP OPI Publication No. 59-97140/1984, in which colored images are obtained by making use of a light-sensitive colored sheet and the corresponding color-separation films are each exposed to light and developed, and the resulting colored images are each transferred onto a support so that a color proof can be formed thereon. The toners for forming the above-mentioned images and the colorants for colored sheets have the advantage that the same coloring materials as printing inks can be used. Therefore, the resulting color proof closely resembles printing in color tone.
However, these processes have the following disadvantages. In the steps for preparing a color proof, images have to be superposed and transferred and it takes a long time to complete the operations and, in addition, the production cost is also expensive.
As for the processes capable of eliminating the above-mentioned disadvantages, there are the processes in which a color proof can be prepared by making use of a silver salt color photographic light sensitive material comprising a white support, such as disclosed in JP OPI Publication Nos. 56-113139/1981, 56-104335/1981, 62-280746/1987, 62-280747/1987, 62-280748/1987, 62-280749/1987, 62-280750/1987 and 62-280849/1987.
In these processes, a proofing image is used in the form of a color image that is formed in the following manner. Plural color-separated black-and-white halftone dot images are prepared by converting a colored original document into plural color-separated halftone dot images. The resulting plural B&W halftone dot images are printed one after another on one sheet of color paper in a contact printing method or the like. The printed images are color developed so that a color image is formed of the dyes produced by the couplers. The resulting color image is to be used as the proofing image.
The above-mentioned technique, however, has the following defects. When the photographic color is approximate printed matter, the density of any black image such as the density of letters is inferior to that of the printed matter. However, when using methods which enhance the black image density to try to approximate the density of the black image such as that of letters to the density of printed matter, the approximation degrees of the color image of the printed matter deteriorate, with the result that it is practically difficult to adjust the densities so that the requirement that both the color and black density approximate printed matter is satisfied.
As for the technique for reducing the above-mentioned defects, there is a well-known technique in which the 4th black printer layer having a spectral sensitivity different from any other layers is arranged, besides the yellow, magenta and cyan color developing layers. This technique is effective as far as an image approximate to a printed matter can be obtained. However, the following problems are raised in this method. Because a black printer layer is added, the total emulsion layer is increased in thickness; half tone dot image reproducibility is caused by sharpness deterioration; physical properties such as curling resistance, deteriorate; manufacturing costs are increased; and the number of processing steps are increased when the black printer layer is separately exposed.